vector is a Random
Access Sequence of heterogeneous typed data structured as a simple
struct where each element is
held as a member variable. vector
is the simplest of the Fusion sequence container (a vector with N elements
is just a struct with N members), and in many cases the most efficient.

Numbered forms will be deprecated in C++11 and it will be provided via
aliasing templates. It means that your partial specialization might be
compile error. You can detect whether it is aliasing templates or not,
using BOOST_FUSION_HAS_VARIADIC_VECTOR.